Having your birthday on Halloween gives you an excuse to have a costume party every year, but a new Yale University study (PDF) seems to indicate that expecting mothers may actively be avoiding giving birth on All Hallows' Eve.

Incidentally, births also seem to go up on Valentine's Day, a revelation that will delight many a conspiracy theorist who believes the chocolate and floral industries are civilization's puppet masters. From the recent study, "Influence of Valentine's Day and Halloween on Birth Timing" from Social Science and Medicine:

On Valentine's Day, which conveys positive symbolism, there was a 3.6% increase in spontaneous births and a 12.1% increase in cesarean births. Whereas, on Halloween, which conveys negative symbolism, there was a 5.3% decrease in spontaneous births and a 16.9% decrease in cesarean births. These effects reached signiﬁcance at p < .0001, after adjusting for year and day of the week. The sample was based on birth certiﬁcate information for all births in the United States within one week on either side of each holiday across 11 years. The Valentine's-Day window included 1,676,217 births and the Halloween window included 1,809,304 births [...]

This study raises the possibility that the assumption underlying the term "spontaneous births," namely, that they are outside the control of pregnant women, is erroneous. For it appears that pregnant women can expedite or delay spontaneous births, within a limited time frame, in response to cultural representations. A previously unnoticed psychophysiological mechanism may explain this pattern: the positive connotations of Valentine's Day may increase a pregnant woman's will to initiate birth and the negative connotations of Halloween may precipitate her will to resist giving birth; both tendencies may then inﬂuence the hormonal mechanism that controls birth timing.

Curious and curiouser! Anyone want to conduct a similar study with Arbor Day? Also, are there any Austrian academics up for researching whether or not Krampus attacks scare children back into the womb on St. Nicholas' Eve?